Case report: psoriatic erythroderma with bilateral osseous bridge across the acetabulum

Abnormal reactions accompanied by bone formation in the osteoarticular region induced by long-term administration of etretinate have been reported. We treated a patient who received continuous treatment of psoriatic erythroderma with etretinate for 7 years, and who had an osseous bridge that extended across the acetabulum over the femur on both sides. The patient experienced a major gait disturbance and eventually was unable to walk. Functional gait was restored by resecting the ossified regions and radiotherapy. Histologic sections of the ossified lesions showed enchondral ossification in the ligament attachment site in the joint margin, with advancing ossification along the articular capsule; the pattern was similar to that in diffuse idiopathic skeletal hyperostosis. This is the first report of an osseous bridge associated with long-term administration of etretinate extending across the acetabulum over the femur on both sides.